The present invention relates to an apparatus and a method for monitoring the conditions of automobile tires. More particularly, the present invention pertains to a system for receiving data transmitted from transmitters, each of which is located in one of the tires of a vehicle.
Wireless tire condition monitoring apparatuses for allowing a driver in a vehicle passenger compartment to check the condition of vehicle tires are known. One such monitoring system includes transmitters and a receiver. Each transmitter is located in one of the wheels and the receiver is located in the body frame of the vehicle. Each transmitter detects conditions such as the air pressure and the temperature of the associated tire and wirelessly transmits the detected information. The receiver receives the information from the transmitters.
Each transmitter is located in one of the tires of a vehicle. The receiver has reception antennas, each of which corresponds to one of the transmitters. Each reception antenna induces a voltage signal that corresponds to the field intensity of radio waves from the associated transmitter. The receiver processes each voltage signal to obtain data.
When receiving data, the receiver must identify the tire in which the transmitter that has transmitted data is located. The tire condition monitoring apparatus disclosed in Japanese Unexamined Patent Publication No. 10-104103 includes a receiver that has such a function. The receiver of the publication switches multiple antennas by a multiplexer circuit such that the voltage induced by a particular one of the reception antennas is valid at a given time. The receiver then determines the reception antenna that has the highest induced voltage level. Since the reception antenna that has the highest induced voltage level is closest to the transmitter that has transmitted the data, the receiver can identify the transmitter.
However, the receiver of the publication must keep the multiplexer circuit activated while waiting for signals from all the transmitters so that the receiver can receive voltage signals from all the antennas, which increases the electricity consumption.
Since the induced voltage of only one of the reception antennas is valid at a given time when identifying the transmitter that has transmitted data, the level of the induced voltage is relatively low. Therefore, accurate identification of a transmitter is difficult.
Accordingly, it is an objective of the present invention to provide a tire condition monitoring apparatus and method that reduce power consumption and accurately identifies the transmitter that has transmitted data.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a tire condition monitoring apparatus for monitoring the conditions of a plurality of tires of a vehicle is provided. The apparatus includes a plurality of transmitters, a plurality of reception antennas, a plurality of level control circuits, a coupler and a controller. Each transmitter is located in one of the tires and transmits data that represents the condition of the corresponding tire by radio waves. The reception antennas are located in the body of the vehicle. Each reception antenna corresponds to one of the transmitters and induces a voltage signal upon receiving radio waves from each transmitter. Each level control circuit corresponds to one of the reception antennas and lowers the level of an associated voltage signal that is induced by the corresponding reception antenna. The coupler synthesizes voltage signals from the level control circuits to form a synthesized voltage signal. The controller controls the level control circuits. When one of the transmitters has transmitted radio waves, the controller commands all the level control circuits to consecutively execute level lowering procedure at intervals such that only one of the level control circuits lowers the level of the associated voltage signal at a time. The controller identifies the level control circuit that lowered the level of the associated voltage signal when the level of the synthesized voltage signal was lowest. The controller determines that the reception antenna that corresponds to the identified level control circuit corresponds to the transmitter that has transmitted radio waves.
The present invention provides another tire condition monitoring apparatus for monitoring the conditions of a plurality of tires of a vehicle. The apparatus includes a plurality of transmitters, a plurality of reception antennas, a plurality of amplifiers, a coupler and a controller. Each transmitter is located in one of the tires and transmits data that represents the condition of the corresponding tire by radio waves. The reception antennas are located in the body of the vehicle. Each reception antenna corresponds to one of the transmitters and induces a voltage signal upon receiving radio waves from each transmitter. Each amplifier corresponds to one of the reception antennas and amplifies an associated voltage signal that is induced by the corresponding reception antenna. The coupler synthesizes voltage signals from the amplifiers to form a synthesized voltage signal. The controller controls the amplifiers. When one of the transmitters has transmitted radio waves, the controller commands all the amplifiers to consecutively stop amplifying at intervals such that only one of the amplifiers stops amplifying at a time. The controller identifies the amplifier that stopped amplifying when the level of the synthesized voltage signal was lowest. The controller determines that the reception antenna that corresponds to the identified amplifier corresponds to the transmitter that has transmitted radio waves.
Further, the present invention provides a method for monitoring the conditions of a plurality of tires of a vehicle. The method includes transmitting data representing the condition of each tire by radio waves from transmitters, each of which is located in one of the tires, inducing a voltage signal upon receiving radio waves from each transmitter in a plurality of reception antennas, each of which corresponds to one of the transmitters, forming a synthesized voltage signal by synthesizing the voltage signals from the reception antennas, consecutively lowering the levels of the voltage signals induced by all the reception antennas such that only one of the voltage signals is lowered at a time when one of the transmitter transmits a radio wave, and determining that an active one of the transmitters is one that is associated with one of the antennas that corresponds to the voltage signal being lowered when the lowest level of the synthesized voltage signal occurs while the voltage signals are being lowered.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.